This invention relates to a radial flow turbine rotor used for a supercharger or the like using high temperature exhaust gas of an internal combustion engine as a drive source and a method of manufacturing the same.
Hitherto, an exhaust gas supercharger has been provided in an internal combustion engine in order to increase the density of air supplied for combustion and to increase the effective pressure of the combustion gas. A radial flow turbine rotor is usually provided in a combustion exhaust gas passage of the supercharger as mentioned. Usually, such a radial flow turbine rotor has a structure comprising a shaft and precision cast heat-resistant steel blades welded to the periphery of the shaft. The maximum permissible temperature of this radial flow turbine rotor is about 650.degree. to 750.degree. C., and the rotational speed is about 100,000 rpm. at most.
With such a radial flow turbine rotor, however, breakage is liable to result at the welded portion of the blade stem when high vibratory stress is produced at a high engine rpm. Further, with the supercharger it is desirable to increase the rpm by taking in high temperature and high pressure combustion exhaust gas and to reduce the stress acting on the blade stem as much as possible. To these ends, it is necessary to construct the entire apparatus with a material, which is light in weight and has excellent mechanical strength and thermal shock resistance. The conventional heat-resistant steels have not been perfectly satisfactory from these standpoints.
Recently ceramic turbine rotors have been developed. For example, a curved blade rotor made of ceramic material is shown at pages 888-891 of CERAMICS FOR HIGH PERFORMANCE APPLICATIONS-II published in 1978 by Brook Hill Publishing Company. The above-mentioned curved blade rotor was made by AME Ltd. in reaction bonded silicon nitride. The main object of making ceramic curved blade rotor is to replace expensive nickel alloys by cheaper, non-strategic materials and to operate the turbine at high temperatures. However, it has been found to be necessary to improve the design of the rotor in making a curved blade rotor of ceramic material.
The inventors have conducted various research and investigations and have found that the time required for finishing a radial flow turbine rotor after sintering can be reduced by obtaining a molding by injection molding using a mold having parting lines corresponding to the edges of blades said molding thus having no burrs on the periphery of the shaft to thereby enhance the efficiency of the turbine provided with the rotor.